Metal-containing polymers have been used extensively in the past to prepare ceramic objects due to the high ceramic "char" yields which result when such polymers are heated to temperatures approaching 1000.degree. C. Such polymers have thus proven useful when used as ceramic powder binders, as precursors to ceramic coatings, as ceramic fiber precursors, and as powder carriers for molding applications. However, despite the high thermal stability of such polymers, and their ability to form ceramic compositions upon thermal decomposition, the mechanical strength of such polymers has limited their utility in applications which require, for example, mechanical strength at temperatures below which conversion to a ceramic occurs.
In contrast, while organic polymers demonstrate marginal high temperature performance, their strength and durability at temperatures below their decomposition temperature have resulted in widespread application where materials such as metals or wood had previously been used.
Block copolymers have been prepared from a variety of organic polymer systems. In addition, block copolymers have been prepared from a variety of inorganic polymer systems. For example, U.S. Pat. No. 5,229,468, entitled "Polymer Precursor for Silicon Carbide/Aluminum Nitride Ceramics" which issued in the name of Jensen on Jul. 20, 1993, discloses recent work relating to novel block copolymers which are ceramic precursors and which incorporate, alternately, a multiplicity of units comprising Al-N bonded segments with a multiplicity of units comprising Si-N bonded segments.
Such block copolymers, whether wholly organic in nature or wholly inorganic in nature, have been shown to exhibit certain desirable characteristics inherent in each of their component compositions.
Recently there has also been some effort in preparing mixed organic/inorganic polymer compositions by, for example, the hydrolysis of Si(OR).sub.4 compounds in which R is an unsaturated, polymerizable organic group such as vinyl or allyl, or an acrylate or methacrylate-based group. Efforts in preparing mixed organic/inorganic polymer compositions have been motivated by limitations which derive from the insolubility of many important engineering polymers within sol-gel solutions. Free-radical curing of such "sol-gel" processed monomers results in mixed systems demonstrating some of the useful properties of the organic components used in the synthesis of the monomers as well as some of the desirable properties of the inorganic components. Typically, such systems comprise semi-interpenetrating networks composed of linear organic polymers and a three-dimensional SiO.sub.2 network. Representative of such an approach is work described by B. M. Novak and C. Davies in Macromolecules, 1991, 24, 5481-5483.
Other work (see, for example, U.S. Pat. No. 4,448,939, entitled "Polyurethanes Prepared Using Poly(Silyldiamines)"), which issued in the names of Fasolka et al., on May 15, 1984), is based on the reaction of --Si--NH--R-- (silyl amine) groups with organic isocyanates. In this work, polyurethane compositions comprising the reaction product of an organic polyisocyanate and a poly(silyldiamine) are described. As shown later herein, these compositions differ from the concepts taught in the present invention.
Similar work by A. A. Zhdanov et. al. in Polymer Science U.S.S.R., Vol. 23, No. 11, pp 2687-2696 (1981), describes the reaction of a nitrogen-hydrogen bond, present in the silyl amine end groups of linear polysilazasiloxanes, with carbonate moieties in mixed polycarbonate silazasiloxane compositions. Such silyl amine end groups are formed by the reaction of hydroxyl groups in the organic fraction of the composition with cyclosilazane rings, resulting in ring opening and concurrent formation of the reactive Si--NH.sub.2 moiety.
U.S. Pat. No. 4,929,704 entitled "Isocyanate- and Isothiocyante-Modified Polysilazane Ceramic Precursors", which issued in the name of Schwark, on May 29, 1990; U.S. Pat. No. 5,001,090 entitled "Silicon Nitride Ceramics from Isocyanate- and Isothiocyante-Modified Polysilazanes", which issued in the name of Schwark, on Mar. 19, 1991; and U.S. Pat. No. 5,021,533 entitled "Crosslinkable Poly(thio)ureasilazane Composition Containing a Free Radical Generator", which issued in the name of Schwark, on Jun. 4, 1991, all disclose the preparation of partially crosslinked organic isocyanate-modified silazane polymers by the initial reaction of less than about 30 weight percent of an organic isocyanate with a polysilazane comprising Si-H bonds so as to effect reaction of the isocyanate with the silicon-nitrogen bond followed by a crosslinking reaction in which a by-product is hydrogen gas. Similarly, U.S. Pat. No. 5,032,649 entitled "Organic Amide-Modified Polysilazane Ceramic Precursors", which issued in the name of Schwark, on Jul. 16, 1991, and U.S. Pat. No. 5,155,181 entitled "(Thio)amide-Modified Silazane Polymer Composition Containing a Free Radical Generator", which issued in the name of Schwark, on Oct. 13, 1992, both disclose the preparation of organic amide-modified silazane polymers by the initial reaction of, for example, less than about 30 wt % of an organic amide with a polysilazane comprising Si-H bonds so as to effect reaction of the isocyanate with the silicon-nitrogen bond followed by a crosslinking reaction in which a by-product is hydrogen gas.
U.S. Pat. No. 3,239,489, entitled "Polyurea-silazanes and Process of Preparation", which issued in the names of Fink et al., on Mar. 8, 1966, describes the one-step preparation of linear as well as crosslinked polymers by the reaction of certain silazanes comprising no nitrogen to carbon bonds within the repeat units of the silazane with di- or poly-functional isocyanates. By reacting such compositions, both linear and crosslinked polymers can be prepared by reacting the di- or poly-functional isocyanates with the N-H bond of the silazane.
To date, no art has disclosed or recognized the importance of: (1) the synthesis of uncrosslinked, but crosslinkable inorganic/organic hybrid polymers or ceramers by the reaction of at least one organic electrophile with at least one metal-nitrogen polymer (e.g., polysilazane, polyalazane, polyborazine, poly(silazane/alazane), etc.); (2) suitable crosslink mechanisms for such polymers in a second processing step; or (3) the crosslinked compositions obtained therefrom. For other silicon-nitrogen based polymers, as well as metal-nitrogen polymers in general, for example, aluminum-nitrogen polymers, boron-nitrogen polymers, and copolymers and terpolymers prepared from, for example, aluminum-nitrogen/boron-nitrogen copolymers, and silicon-nitrogen/boron-nitrogen copolymers, no systems are known.
Furthermore, the utility of such inorganic/organic hybrid polymers or ceramers in applications not involving a pyrolysis conversion to a ceramic material has never been contemplated.
The art is replete with examples of organic polymers utilized for many different traditional applications. However, a need exists to expand the use of polymers or polymer-like materials into some non-traditional areas.
For example, much effort has been focused on enhancing the elevated temperature properties of organic polymers to permit such polymers to function effectively in various high temperature environments. However, the elevated temperature performance of organic polymers is limited by the tendency of organic polymers to degrade and/or decompose into unacceptable or undesirable elements.
Moreover, certain uses of organic polymers are not practical because such polymers typically lack flame retardant properties and in some instances even function as fuel to sustain combustion. Accordingly, the use of combustible polymers for many applications may not be acceptable or permissible.
Further, many organic polymers exhibit unacceptable degradation when exposed to ultraviolet ("UV") radiation. The inherent susceptibility of such polymers to UV radiation is caused by the bonds in the polymer breaking because UV radiation possesses energy levels corresponding to some of the bond energies within the polymers. The correspondence of the bond energies to UV radiation causes organic polymers to degrade via, for example, a bond scission mechanism. Efforts to reduce the susceptibility of organic polymers to UV radiation has included, for example, the incorporation of expensive ingredients that attempt to absorb harmful UV radiation. The cost for incorporating these ingredients can be prohibitive.
Further, many organic polymers have been excluded from certain applications where the polymers lack adhesive properties, even though certain other properties of the polymers may be desirable. Some of the applications which require polymers to exhibit certain desirable adhesive properties include those applications where a polymer is placed as a coating upon a substrate material. If the polymer lacks adhesive properties, the polymer coating may flake or spall from the substrate material. Additionally, in certain situations it may be desirable to form a composite material from a polymer and another reinforcing material. In this case, it is desirable for the polymer to bond or adhere to the reinforcing phase in order to form a desirable polymer matrix composite material.
Accordingly, for these and other reasons, organic polymers have been relegated to applications which do not expose the polymers to their weakness. Thus, the inherent weaknesses exhibited by polymers has kept polymers from realizing even broader applications.
The art also contains certain examples of inorganic polymers, with an emphasis in the art being placed on certain preceramic polymers. These inorganic polymers have been developed primarily with an emphasis on their char or conversion yield. Specifically, a high char yield has been a primary goal of this type of polymer because the conversion of polymer to ceramic needed to be maximized. This emphasis on optimum conversion has resulted in the use of these preceramic polymers as precursors to ceramic. Additionally, any practical use of the preceramic polymers as polymers, per se, has been discouraged because of their relatively poor mechanical properties exhibited by preceramic polymers. Moreover, some preceramic polymers require stringent storage conditions. For example, some inorganic preceramic polymers require refrigeration to suppress reactions that would otherwise occur spontaneously at room temperature or even below room temperature. Further, processing of some inorganic preceramic polymers is complicated by their viscous character. In turn, this viscous character typically requires expensive pressure processing equipment. Accordingly, due to the aforementioned considerations, the use of perceramic polymers for anything other than precursors to ceramic materials has not been considered and/or has been impractical.
The present invention capitalizes on foresight and the understanding of the limitations exhibited by wholly organic or wholly inorganic polymers. To this end, the present invention recognizes the inherent limitations exhibited by each class of organic and inorganic polymers. However, it has been unexpectedly discovered that certain synergistic effects can be realized by combining organic and inorganic polymers in a novel manner to achieve a new class of materials--hybrid polymers or ceramers.
Accordingly, the present invention satisfies a long felt need by overcoming the above-discussed limitations associated with wholly organic polymers by combining synergistically organic polymers and inorganic polymers. Specifically, the present invention results in, among other things, polymers which have elevated temperature applicability; polymers which adhere to various surfaces, especially to inorganic surfaces, heretofore uncharacteristic of organic polymers (e.g., not only do the hybrid polymers or ceramers provide excellent matrices for reinforced composites, but the hybrid polymers or ceramers facilitate the joining of any type and/or number of materials to allow the combination of materials heretofore considered difficult, if not impossible, to join); polymers which exhibit superior UV radiation resistance; and polymers which exhibit flame retardant characteristics.
Further, the present invention satisfies a long felt need for materials possessing characteristics of inorganic polymers combined with simple processing. The present invention satisfies this need by providing hybrid polymers or ceramers from mixtures including, for example, low viscosity liquids that are inexpensively processed into the most complex of shapes and then transformed into solids. For these and many unstated reasons, the novel compositions of the invention, and materials derived therefrom, satisfy a long felt need for a new class of materials applicable in ways that transcend traditional notions applicable to either wholly organic and/or wholly inorganic polymers.